1. Field of the Invention
The present invention relates to a recording liquid, generally called ink, adapted for use in writing utensils or ink jet recording apparatus, and a method for producing such recording liquid, and more particularly a recording liquid not causing clogging of the tip of such utensils or ejection orifice and a method for producing the same.
2. Description of the Prior Art
For use in writing utensils such as felt pen or fountain pen there are already known inks composed of various dyes or pigments dissolved or dispersed in liquid media such as water or organic solvents. Also the use of similar inks is already known in so-called ink jet recording in which the ink contained in a recording head is ejected from ejection orifices for recording by means of mechanical vibration by a piezoelectric element, electrostatic attractive force by a high voltage or thermal energy.
A typical ink for writing utensils or ink jet recording is basically composed of three components; a water-soluble dye, water as the solvent for said dye, and glycols for preventing evaporation. For such water-soluble dye principally employed are direct dyes and acid dyes because of satisfactory fastness and color after recording. Such dyes are originally produced for fiber dying and generally contain a considerably amount of salts such as sodium chloride, sodium sulfate or sodium acetate which are by-products of dye synthesis or are intentionally added as salting out agent, diluting agent or level dying agent.
The recording ink made of dyes containing such salts is associated with the following drawbacks. Such salts generally affect the stability of dissolution of dyes in the ink, eventually leading to the aggregation or precipitation of the dyes. Also in the ink jet recording, such salts become precipitated if the ink composition is altered by the evaporation thereof in the vicinity of the ejection orifice. These phenomena lead to the clogging of orifice, the most undesirable trouble particularly in the ink jet recording. Although there have been proposed various measures for preventing the clogging of the point of writing utensils and ejection orifices of ink jet recording apparatus, none has ever referred to the salt concentration in the ink.
The dye concentration in an ink easily inducing such clogging has to be lowered, thus giving rise to an insufficient recording density, with unsatisfactory image quality and deficient light fastness of the recorded image.